Re: [patch v2 05/14] genirq: Expose nr_irqs in core code

[Radu Rendec <radu@rendec.net>]

On Fri, 2026-03-20 at 14:21 +0100, Thomas Gleixner wrote:
> ... to avoid function calls in the core code to retrieve the maximum number
> of interrupts.
> 
> Signed-off-by: Thomas Gleixner <tglx@kernel.org>
> Reviewed-by: Dmitry Ilvokhin <d@ilvokhin.com>
> ---
>  kernel/irq/internals.h |    1 +
>  kernel/irq/irqdesc.c   |   28 ++++++++++++++--------------
>  kernel/irq/proc.c      |    2 +-
>  3 files changed, 16 insertions(+), 15 deletions(-)
> 
> --- a/kernel/irq/internals.h
> +++ b/kernel/irq/internals.h
> @@ -21,6 +21,7 @@
>  
>  extern bool noirqdebug;
>  extern int irq_poll_cpu;
> +extern unsigned int total_nr_irqs;
>  
>  extern struct irqaction chained_action;
>  
> --- a/kernel/irq/irqdesc.c
> +++ b/kernel/irq/irqdesc.c
> @@ -140,14 +140,14 @@ static void desc_set_defaults(unsigned i
>  	desc_smp_init(desc, node, affinity);
>  }
>  
> -static unsigned int nr_irqs = NR_IRQS;
> +unsigned int total_nr_irqs __read_mostly = NR_IRQS;
>  
>  /**
>   * irq_get_nr_irqs() - Number of interrupts supported by the system.
>   */
>  unsigned int irq_get_nr_irqs(void)
>  {
> -	return nr_irqs;
> +	return total_nr_irqs;
>  }
>  EXPORT_SYMBOL_GPL(irq_get_nr_irqs);
>  
> @@ -159,7 +159,7 @@ EXPORT_SYMBOL_GPL(irq_get_nr_irqs);
>   */
>  unsigned int irq_set_nr_irqs(unsigned int nr)
>  {
> -	nr_irqs = nr;
> +	total_nr_irqs = nr;
>  
>  	return nr;
>  }
> @@ -187,9 +187,9 @@ static unsigned int irq_find_at_or_after
>  	struct irq_desc *desc;
>  
>  	guard(rcu)();
> -	desc = mt_find(&sparse_irqs, &index, nr_irqs);
> +	desc = mt_find(&sparse_irqs, &index, total_nr_irqs);
>  
> -	return desc ? irq_desc_get_irq(desc) : nr_irqs;
> +	return desc ? irq_desc_get_irq(desc) : total_nr_irqs;
>  }
>  
>  static void irq_insert_desc(unsigned int irq, struct irq_desc *desc)
> @@ -543,7 +543,7 @@ static bool irq_expand_nr_irqs(unsigned
>  {
>  	if (nr > MAX_SPARSE_IRQS)
>  		return false;
> -	nr_irqs = nr;
> +	total_nr_irqs = nr;
>  	return true;
>  }
>  
> @@ -557,16 +557,16 @@ int __init early_irq_init(void)
>  	/* Let arch update nr_irqs and return the nr of preallocated irqs */
>  	initcnt = arch_probe_nr_irqs();
>  	printk(KERN_INFO "NR_IRQS: %d, nr_irqs: %d, preallocated irqs: %d\n",
> -	       NR_IRQS, nr_irqs, initcnt);
> +	       NR_IRQS, total_nr_irqs, initcnt);
>  
> -	if (WARN_ON(nr_irqs > MAX_SPARSE_IRQS))
> -		nr_irqs = MAX_SPARSE_IRQS;
> +	if (WARN_ON(total_nr_irqs > MAX_SPARSE_IRQS))
> +		total_nr_irqs = MAX_SPARSE_IRQS;
>  
>  	if (WARN_ON(initcnt > MAX_SPARSE_IRQS))
>  		initcnt = MAX_SPARSE_IRQS;
>  
> -	if (initcnt > nr_irqs)
> -		nr_irqs = initcnt;
> +	if (initcnt > total_nr_irqs)
> +		total_nr_irqs = initcnt;
>  
>  	for (i = 0; i < initcnt; i++) {
>  		desc = alloc_desc(i, node, 0, NULL, NULL);
> @@ -862,7 +862,7 @@ void irq_free_descs(unsigned int from, u
>  {
>  	int i;
>  
> -	if (from >= nr_irqs || (from + cnt) > nr_irqs)
> +	if (from >= total_nr_irqs || (from + cnt) > total_nr_irqs)
>  		return;
>  
>  	guard(mutex)(&sparse_irq_lock);
> @@ -911,7 +911,7 @@ int __ref __irq_alloc_descs(int irq, uns
>  	if (irq >=0 && start != irq)
>  		return -EEXIST;
>  
> -	if (start + cnt > nr_irqs) {
> +	if (start + cnt > total_nr_irqs) {
>  		if (!irq_expand_nr_irqs(start + cnt))
>  			return -ENOMEM;
>  	}
> @@ -923,7 +923,7 @@ EXPORT_SYMBOL_GPL(__irq_alloc_descs);
>   * irq_get_next_irq - get next allocated irq number
>   * @offset:	where to start the search
>   *
> - * Returns next irq number after offset or nr_irqs if none is found.
> + * Returns next irq number after offset or total_nr_irqs if none is found.
>   */
>  unsigned int irq_get_next_irq(unsigned int offset)
>  {
> --- a/kernel/irq/proc.c
> +++ b/kernel/irq/proc.c
> @@ -447,7 +447,7 @@ int __weak arch_show_interrupts(struct s
>  }
>  
>  #ifndef ACTUAL_NR_IRQS
> -# define ACTUAL_NR_IRQS irq_get_nr_irqs()
> +# define ACTUAL_NR_IRQS total_nr_irqs
>  #endif
>  
>  #define ZSTR1 "          0"

Nit: This is modified again in the next patch, so it doesn't matter.
But for the purpose of this patch in isolation, looking at where
ACTUAL_NR_IRQS is used, in show_interrupts() the nr_irqs variable
should also be initialized to total_nr_irqs to avoid the extra function
call.

Reviewed-by: Radu Rendec <radu@rendec.net>